1. Field of the Invention
The present invention relates to a thin film deposition apparatus for use in a semiconductor manufacturing process or the like, and in particular to improvement of coverage to a bottom surface and a side surface of a fine groove or a pore when a thin film, such as a diffusion barrier film is deposited onto a substrate having the fine groove or the pore (hereinafter referred to as the contact hole) with a higher aspect ratio.
2. Description of the Prior Art
In semiconductor devices such as LSI, an evaporated film tends to have a finer structure because of highly integrated devices. As a result, there has been an increase in the use of relatively deep holes or through-holes. Such holes have an aspect ratio (AR=ration of hole depth to hole diameter) of 1 or more
FIG. 1 is a sectional view showing a structure of a thin film deposition apparatus using a conventional sputtering method, disclosed in, for example, Japanese Patent Application Laid-Open No. 4-64222. In FIG. 1, reference numeral 1 indicates a vacuum tank, and 2 indicates an exhaust passage extending from a bottom portion of the vacuum tank 1. The exhaust passage 2 is connected to a high-evacuation pump (not shown). Further, reference numeral 3 indicates an evaporation material made of, for example, high purity titanium (Ti) when a diffusion barrier film is deposited, or high purity aluminum (Al), or an alloy essentially containing aluminum, when an interconnecting film is deposited. The evaporation material 3 is supported by a holder 5 which is disposed in the vacuum tank 1 through an insulating support member 4. Reference numeral 6 indicates a substrate mounted on a substrate holder 8 including a heater 7. The substrate 6 should be chosen such that the evaporation material 3 is larger than the substrate 6 in dimension. For example, an evaporation material 3 having a diameter in an approximate range of 250 to 300 mm is employed when a substrate 6 having a diameter of 200 mm is employed.
Reference number 9 indicates a sputtering power source connected to the holder 5, and 10 indicates a glow discharge forming between the evaporation material 3 and the substrate 6. The discharge is maintained by a high purity argon (Ar) gas which is introduced through a gas introducing valve 11. When titanium nitride (TiN) is deposited as the diffusion barrier film, a mixed gas of the high purity argon gas and high purity nitrogen is introduced. Reference numeral 12 indicates a shield which limits a generating position of the glow discharge 10, and prevents abnormal discharge to the vacuum tank 1 or the like.
A description will now be given of the thin film deposition method using the conventional apparatus constructed as set forth above. The substrate 6 onto which the thin film is deposited is mounted onto the substrate holder 8, and the vacuum tank 1 is evacuated, by using the high-evacuation pump, to a pressure level of 10.sup.-4 Pa. Subsequently, the high purity argon gas is introduced by adjusting the gas introducing valve 11 until the pressure in the vacuum tank 1 becomes 0.1 Pa. Then, the sputtering power source 9 is actuated to generate the glow discharge between the evaporation material 3 and the substrate 6. Accordingly, an argon ion in a discharge space sputters the evaporation material 3, turning out particles 3a of the evaporation material 3. Thus, these particles 3a of the evaporation material 3 are deposited on the substrate 6 to form the thin film. In such a sputtering method, a distance between the evaporation material 3 and the substrate 6 is about 10 cm, pressure at a time of thin film deposition is about 0.6 Pa, and a mean free path (.lambda.) of the evaporation material particles 3a is about 1 cm. Therefore, it is possible to find that the Knudsen number K.sub.n =.lambda./H is 0.1 depending upon a ratio of the mean free path .lambda. of the interconnecting material particles 3a to the distance H between the evaporation material 3 and the substrate 6. The evaporation material particles 3a ejected from the evaporation material 3 can reach the substrate 6 while being scattered by a discharging gas or a residual gas.
A description will now be given of a method of depositing a multilayer interconnection film into the contact hole by using the sputtering method as set forth above with reference to FIGS. 2(A) to 2(D). In FIG. 2(A), reference numeral 6 indicates a substrate made of silicon or the like, 12 indicates a diffusion layer, 13 is an insulating film made of silicon dioxide (SiO.sub.2) having a thickness of 1 .mu.m by using, for example, a CVD method, and a contact hole 13a is provided in the insulating film 13 having a diameter of about 0.6 .mu.m, a depth of 1 .mu.m, and an aspect ratio of 1.7. In the first step, the high purity titanium is employed as the evaporation material 3 to deposit a diffusion barrier film 14 of the titanium nitride according to a reactive sputtering method to sputter the evaporation material 3 using a discharge gas in which the argon and the nitrogen are mixed in a ratio of 1:1 as shown in FIG. 2(B). In a second step, an aluminium-silicon-copper alloy is employed as the evaporation material 3, and the argon serving as the discharge gas is introduced into the vacuum tank 1 and a substrate temperature is set to room temperature to sputter the evaporation material 3 so as to form a first interconnecting film 15 as shown in FIG. 2(C). Further, in a third step, the evaporation material 3 made of an aluminium alloy is sputtered while the substrate is rapidly heated up to the substrate temperature of 500.degree. C., resulting in a second interconnecting film 16 formed by plugging up the contact hole 13a with the interconnecting material as shown in FIG. 2(D).
In the sputtering method as set forth above, the particles of the evaporation material collide with the discharge gas, resulting in low directivity of the particles. It is known that an incident angle distribution of the evaporation material particles on the substrate is determined by the cosine law. That is, in the sputtering method, many particles are diagonally incident on the substrate, and a few particles can reach a bottom portion of the contact hole. Further, it is difficult to deposit the diffusion barrier film or the interconnecting film with good coverage in an contact hole having the aspect ratio of 2 or more. When an evaporation method is employed as in the case of an interconnecting film deposition apparatus disclosed in, for example, Japanese Patent Application Laid-Open No. 2-271634, it is generally considered that the evaporation method can exhibit good directivity of the particles of the interconnecting material. However, it is difficult to deposit the diffusion barrier film or the interconnecting film onto a bottom surface of the contact hole with good coverage due to a shadowing effect as set forth above.
Hence, another method is examined where the substrate is heated to enhance fluidity of the interconnecting material so as to pour the material into the contact hole. For example, when the aluminium alloy is employed as the interconnecting material, the interconnecting material is sputtered while the substrate is heated up to a temperature range of 400.degree. to 500.degree. C., and the interconnecting material is poured into the contact hole so as to improve the coverage.
The conventional thin film deposition apparatus is constructed as set forth above, and the thin film is deposited as set forth above. Therefore, only when the evaporation material has a relatively low melting point, it is possible to employ the method of improving the coverage of the interconnecting film or the diffusion barrier film by heating the substrate during or after the evaporation. Consequently, there are problems as follows: The method can not be applied to the deposition of the diffusion barrier film using a refractory material such as the titanium nitride having an enhanced diffusion barrier performance since a heating temperature is limited in the LSI manufacturing process employing a silicon substrate. Further, it is difficult to deposit the diffusion barrier thin film having good coverage in the contact hole since the contact hole has a higher aspect ratio when an integrated circuit is developed to have a more finer structure, and a higher integrated structure.